The handling of organic sludge materials, such as residential or commercial sewage, or animal slaughterhouse refuse, has lately become a matter of great public concern, as the disposal sites for such materials are limited in supply and capacity. Furthermore, such waste materials have been found to pose safety or health hazards if not properly handled and disposed.
As it is not uncommon to encounter waste materials which include up to 94% water by weight, it has been found advantageous to extract as much water from the waste materials as possible in order to reduce later handling and disposal costs. However, a trade-off has been recognized between the savings in handling and disposal costs, and the cost of removing the water from the waste.
Various prior art methods and apparatus for the removal of water from solid sludge material have been utilized. One type of apparatus mechanically separates water from solid waste by the use of a rotating drum having a filtering screen about its circumferential surface. Waste is inserted inside the drum, and the drum is rotated such that centrifugal force drives the waste material through the filtering screen, which preferably retains the solids and allows the water to pass. A second type of mechanical separation is by use of a mechanical press which forces waste material against a filtering screen, which likewise preferably retains the solids and allows the water to pass. Yet another type of water removal is by natural evaporation, which is usually done by placing the sludge in large drying pools which are exposed to sunlight. The water evaporates from the sludge, and the solid wastes are left behind.
However, these prior art apparatus and methods are both inefficient and time-consuming. The previously-mentioned mechanical separation methods include the use of large and expensive machinery, which is expensive to operate and maintain. These machines may not be continuously operated, and may have significant down times during cleaning. Furthermore, it is possible that the filtered water may still include some contaminate. The natural evaporation method, although requiring little operating machinery, requires a large amount of space, and is a very time-consuming project, often taking several weeks.
It has been known to provide apparatuses which heat moisture-laden waste materials in order to encourage evaporation of water from the waste. U.S. Pat. No. 3,744,145 to Maxwell is an example of such an apparatus. Maxwell discloses the use of a plurality of parallel troughs which accept waste material. A plurality of corresponding fingers are movable within the troughs which push the waste material along the troughs. The troughs are heated in order to dry the waste material.
Although the use of heat is effective in drying waste materials, the heating process must be closely monitored if it is preferred to use the waste material for fertilization purposes, as heat tends to destroy preferably proteins in the waste material. It should be understood that in the Maxwell apparatus, this was not a concern as Maxwell disclosed the use of an incinerator at the exit end of the dryer which burned the waste materials.
Therefore it may be seen that there is a need for an apparatus or method which removes moisture from sludge materials in a time- and cost-effective manner, without destroying desirable proteins in the sludge.